It has been known basically to vary the simulated resistance to manual steering effort by way of increased resistance in response to increase in vehicle speed. For example, the U.S. patent to Uchiyama et al, U.S. Pat. No. 3,690,400 shows such an arrangement and other patents in the field are German DE-PS No. 21 27 070 and German DE-GM No. 80 29 580.
In particular, the patents or applications of Armin Lang, assigned to the present assignee, viz., German DE No. 31 22 370 (application), which became the present U.S. Pat. No. 4,438,827 and U.S. Pat. No. 4,462,478, are of particular pertinence as background art in that they show arrangements utilizing control valve means such as integral coaxial piston valves and separately movable piston valves, including fixed throttles in lines from the chambers of a double acting servomotor to reaction chamber of the valves for exerting pressure forces in opposite directions.
U.S. Pat. No. 4,438,827 is relied on for the closest background of the present invention and is hereby incorporated by reference along with U.S. Pat. No. 4,186,818 of Jablonsky, likewise assigned to the present assignee.
Thus, in the disclosure herein it will be understood by persons familiar with the art that the mechanical force which returns the reciprocal valve means to a neutral position after a steering operation is effected by springs such as 62, 62A, as shown in U.S. Pat. No. 4,186,818, FIG. 3. Also, the arrangement of a rotary valve housing which carries the reciprocal valves, as used in most of the modifications herein is shown in that patent together with conventional structure as shown to complete an operative booster steering device familiar to persons skilled in the art.